It is common for current axial flow gas turbine engines to employ variable stator vanes to vary the flow characteristics of, in particular, the compressor.
For example, the inlet guide vanes are used to widen the design performance of the compressor by changing the air swirl velocity component of inlet air to match the speed of the compressor. This variation of swirl can be achieved by mounting the inlet guide vanes on simple pivots and regulating the angular setting of the vanes in accordance with the compressor speed.
However, if the whole vane is turned the leading edge incidence ceases to be optimal causing significant losses and some of the potential benefits are lost. It is often the case that the swirl angle of air entering the front face of the stator ring is substantially constant. In the case of the first stage fan inlet guide vanes the angle may even be zero, i.e. air flow is virtually wholly axial. The leading edge portion of the guide vane is, therefore, preferably fixed.
Variable camber guide vanes with fixed leading edge incidence are known from GB Patent No 736,796 Rolls-Royce Ltd in which the stator blades are divided longitudinally into a fixed leading edge portion and a relatively pivotable trailing edge for imparting the adjustable swirl characteristics. The trailing part of the vanes are pivotally mounted in the outer engine casing structure, and may be mounted also in the inner stator structure.
The angularly adjustable parts of the whole stator ring are preferably interconnected for simultaneous angular adjustment by means of a coupling ring attached to radius arms carried by spindles which extend from each vane.
A similar type of arrangement is also know from GB Patent No 774,501 in the name of PowerJets (Research and Development) Limited. In this the stator ring is located in the turbine entry and the fixed leading edge part receives substantially axially flowing hot gas from a combustor outlet.
A problem inherent in this type of arrangement arises from an abrupt transition in the airfoil surfaces of the vane at the junction between the fixed and pivoted parts of the structure which precipitate breakaway of the airflow. The present invention attempts to solve this problem by providing a variable camber vane in which the full turning effect is achieved more progressively.